Electron discharge device



Se t. 27, 1932. A. w. HULL ELECTRON DISCHARGE DEvfCE Filed April 10. 1928 Inventor: Aibert W. Hull,

H His' Attorney,

Patented Sept. 27, 1932 UNITED STATES PATENT OFFICE ALBERT w. HULL, or scnnnnc'mny, nnw YonK, assreuon no criminal. ELEGTRIO COMPANY, A

CORPORATION OF NEW YORK ELECTRON DISCHARGE DEVICE Application filed April 10,

The present invention relates to electron discharge devices of the type which are provided-both with cooperating electrodes for maintaining an electron discharge and also an input electrode (or grid) and it comprises in particular a novel construction and arrangement of the input electrode.

Electron discharge devices which are provided with input electrodes may be divided into two general classes: (1) Electric discharge devices in which the space current s mainly electronic and is continuously variable by variations in potential of the input electrode. in some cases such devices contain sufficient gas to modify by its ionization the electron current for special purposes, such as the detection of radio signals, but ionization of gas, generally speaking, is a secondary phenomenon in this class of devices. The. voltage drop increases with an increase of current, that is, the volt-ampere characteristic is positive. (2) Discharge devices, 1n which a sufficiently high negative potential on an input electrode entirely prevents the iiow oi space current, but a lower negative charge or a positive grid charge permits space current to flow between the main electrodes, the grid potential after the establishment of current flow having no efiect. Such devices contain gas, or vapor, at a pressure high enough to cause the resulting ionization to neutralize space charge completely and operate with a voltage between anode and cathode as low or lower than the ionization potential of the residual gas. The current voltage characteristic of such devices is generally negative, that is the voltage drop decreases with an increase of current. The discharge is considered as being arc-like in its characteristics.

In the second class of discharge devices, to which my invention relates, the grid heretofore has been located close to and around the anode or has extended between the walls of the container transversely across the discharge space, at some distance from the oathode. In either case, the cathode is surrounded in large part by the container walls, and exposed to the electrostatic action of these walls.

I have discovered that these container walls, which ordinarily consist of glass, be-

-with suitable electrical 1928. Serial No. 268,975.

come charged negatively and affect the operation or" the device in an objectionable manner.

I have also discovered that when the grid surrounds the cathode, as shown herein, the control of the current requires the expenditure of much less energy in the input than in the previously used constructions.

My invention will be better understood by reference to the accompanying drawing and the following description of a specific embodiment, namely, a three-electrode form of rectifier or valve tube. The drawing shows such a tube in perspective in Fig. 1, to ether connections or its operation. Certain structural features of the cathode have been shown in Fig. 2, which is a vertical section of a cathode shown somewhat enlarged.

The tube shown in Fig. 1 comprises an circuit elongated and somewhat bulbous glass receptacle 1 into which are mounted the oathode 2, which will be described in detail presently, the anode 3, which consists of a disk of a graphite, nickel or other suitable material, and the input electrode 4:, which will be briefly referred to as the grid. The discharge space contains an attenuated gas or vapor as further described below.

The cathode which may consist of nickel, or iron comprises, as shown in Fig. 2, a central enclosure 5, upon which are mounted by welding or otherwise outwardly extending vanes 6 and inside of which is contained a heater 7, consisting of a helically coiled wire of tungsten, or other suitable refractory metal. The cylinder 5 is lined with suitable refractory material 8, such as alumina or thoria, which prevents short-circuiting of the coiled cylinder 7 during operation of the device.

Electrical connections to the heater 7 may be made in any convenient way, such as through a terminal conductor 9 to one end and by joining the heater by welding or riveting to the end wall 10 of the cylinder 5. The electrical circuit is completed through one or both of the conductors 11-12 which are joined to an outer cylinder 13 which encloses and is joined to the vane 6. This cylinder 13 not only in this way completes the electrical circuit but has for a main function toreduce the radiation heat losses from the vane6 and thus to conserve the heat current required to maintain the cathode at a desired elevated temperature. Preferably theexterior of the cylinder 13' is ,polished to reduce heat. radiation. The vanes 6 and adjoining surfaces within the enclosure 13, are coated with a suitable material of high electron emissivity, such as a rare earth metal, an alkaline earth metal or a compound of an alkaline earth metal. For example, the cathode structure may be coated with barium carbonate and then heated while mounted within the envelope 1 to a temperature adjacent the melting point of nickel to decompose the barium carbonate, and produce a material of high electron emissivity. Preferably the envelope 1 is evacuated during this forming process and the temperature of the cathode members during the forming is carried as close as is practicable to the i melting point of nickel. The leading-in conductors 9, 11 and 12 are sealed into a glass stem 41 in the usual well understood manner and are joined to suitable external electrical contacts 1415 of a base 16. Electrical connection to the anode 3 is made as usual through the conductor 17, sealed in the glass stem 18, and joined to an external metal cap 19. The features of cathode construction herein described are covered by my copending application Serial No. 156,713 filed December 23, 1926, and also application Serial No. 268,976 filed on April 10, 1928 by myself jointly with William A. Ruggles.

The grid 4 consists of sheet metal cupshaped member provided with a plurality of holes 21, the number and area of which depend upon the amplification characteristic desired in the device.

The location of the grid surrounding the cathode and spaced closely adjacent thereto causes the cathode to be entirely shielded by the grid from the electrostatic influence of the walls of the envelope. It will be observed from the drawing that the grid is so constructed and arranged that no lines of electric force can pass from the walls to the cathode.

The grid is connected to wires 22, 23 which lead to a collar 24 which encircles the stem 41 and thus supports the grid. The wire 23 is led through the wall of the envelope 1 to an external contact device 25. A disk 27, consisting of nickel, or other heat reflecting material, may be mounted upon the stem 41 so as to shield the envelope structure at the base of the lamp from the direct heat radiation of the cathode.

The evacuated envelope may contain a small quantity of mercury or other suitable vaporizable material which furnishes a desired ionizable atmosphere for the lamp.

The heat shielding action of the disk 27 prevents excessive heating of this vaporizable substance. In a device such as shown and described the'pressure of the mercury vapor during operation is ordinarily about 10 microns. A rare gas, such as argon likewise may be used as the ionizing medium. The space current due to gas lonization has a negative or arc-like volt-ampere characteristic. The drawing shows for illustrative purposes a system of connections suitable for use in connection with the described tube.

The cathode 2 and the anode 3 are shown respectively connected to the conductors 30, 31 leading to a suitable source of alternating current such as the generator 32. An external load device may be included in this circuit as represented in the drawing by the coil 26 of a relay magnet, or other current consuming means. The cathode conductors 30 and 33 are connected to a low potential transformer winding 34 the primary 35 of which is in the main external load circuit. The grid circuit 36 is connected at one end to the cathode and at the opposite end to the grid terminal 25 through a secondary transformer winding 37. Included in the grid circuit is a resistance 38 which is shunted by a variable neutralizing condenser 39. The condenser 39 neutralizes the capacity which exists between the grid and the anode.

The described device and circuit connections may be used for example to control a power current in a load, for example, a lighting circuit may be controlled through the operations of a photoelectric cell 40. When the light shining upon the active electrode of the photoelectric cell is reduced. then the current through the cell is correspondingly reduced. This current tends to charge the grid positively while the current through the resistor 38 tends to charge the grid negatively. When the current through the photocell predominates, then the grid will be positive during the half cycle when current can flow. Hence, a flow of rectified current in the load circuit 31 occurs and when the flow of current has once been started, the grid has no longer any effect, or, in other words, can neither reduce nor stop the space current through the device. Removing the anode voltage, however, will stop the flow of space current. As the application of anode voltage of proper polarity to permit proper flow of current through the rectifier occurs in short pulsation due to the alternating character of the supply current, the flow of load current is controlled by the grid for each pulsation.

Devices of the described character operating with an average current of about 5 amperes and an anode voltage of 220 volts, has been reliably controlled by the application of energy of about of a microwatt to the grid.

&

What I claim as new and desire to secure vapor in the envelope during operation to Y by Letters Patent of the United States is:

1. An electrical discharge device comprising a receptacle, a charge of gas contained therein at a sufficiently high pressure to cause the discharge therethrough to have arc-like characteristics, an anode, a cathode, and a cup-shaped perforated control electrode closelysurrounding said cathode.

2. An electrical discharge device comprising a bulbous evacuated envelope, an anode and a cathode sealed into opposite points in said container and being spaced apart therein in juxtaposed relation, a cup-shaped grid electrode surrounding said cathode and being spaced more closely to the cathode than to o the anode, both said cathode and said grid electrodes being spaced away from the walls of said envelope. a quantity of mercury contained therein, the envelope and contained electrodes being so proportioned in size and shape as to cause the pressure of mercury vapor in the envelope during operation to be of the order of aboutlO microns.

3. An electrostatically controlled are discharge devicehaving electrodes including a thermionic cathode, a cup-shaped control electrode having aplurality of holes and means for supporting said electrode in a position to enclose said'cathode.

4. An electrical discharge device comprising a receptacle, a charge of gas contained therein at a sufficiently high pressure to cause the discharge therethrough to have an arclike characteristic, an anode, a cathode positioned at the opposite end of the receptacle from the anode, and means for shielding the cathode from external electric fields, said means comprising a cup-shaped control member enclosing the cathode.

5. An electrical discharge device comprising a receptacle, a charge of gas contained therein at a sufliciently high pressure to cause the discharge .therethrough to have arc-like characteristics, an anode, a cathode positioned at the opposite end of the receptacle from the anode, and means for intercepting substantially completely lines of force from said receptacle to said cathode, said means comprising a control electrode which surrounds the cathode and is spaced closely adjacent thereto.

6. An electrical discharge device comprising abulbous evacuated envelope, an anode and a cathode sealed into opposite points in said container and being spaced apart therein in juxtaposed relation, a grid electrode surrounding said cathode and being spaced away from the walls of said envelope whereby the lines of force from said envelope to said cathode are substantially completely intercepted, a quantity of mercury contained in the envelo e, said envelope and contained mg so proportioned in size and shape as to cause t e pressure of mercury be of the order of about 10 microns.

In witness whereof l have hereunto set my hand this 9th day of April 1928.

ALBERT W. HULL. 

